1. Field of the Invention
The present invention relates to a combustion-engined setting tool for driving fastening elements, such as nails, bolts, pins, etc . . . in a constructional component and including a combustion chamber, a fuel source, a fuel conduit for connecting the fuel source with the combustion chamber, at least one metering device arranged in the fuel conduit; and a control device for actuation of the metering device.
2. Description of the Prior Art
The setting tools of the type described above are operated on gaseous or liquid fuels which are combusted in a combustion chamber and drive a drive piston for driving in fastening elements.
Generally, the problem with fuel consists in admixing, in each operational cycle, of a proper amount of air or oxygen, which constitutes oxidation means, to the fuel. The amount of oxygen, which is available for combustion, depends to a great extent on the surrounding temperature, air pressure, and air humidity. The necessary amount of fuel, which takes part in combustion, changes within a wide range, dependent on the above-mentioned parameters, up to 40% in an extreme case. The variations of the amount of fuel adversely affect the combustion of the air-fuel mixture when the air-fuel mixture contains too much fuel or too little fuel.
German Publication DE-42 43 617A1 discloses a setting tool in which in each working cycle, a gas inlet valve opens mechanically, with an amount of fuel fed from a fuel source into a storage space through the valve being dependent on the surrounding conditions. In this way, the pressure and, if necessary, the temperature is (are) equalized with that (those) of the surrounding air, whereby a proper air-fuel mixture is fed into the combustion chamber. The fuel is fed from the storage space at a predetermined time.
The drawback of the tool of DE 42 43 617 A1 consists in that the dependence on the parameters of the surrounding air can lead to loss of fuel. Further, the pressure in the metering chamber is not controlled.
European Publication EP-0 597 241 B1 discloses a combustion-engined setting tool in which fuel is fed from a fuel source to the combustion chamber through a normally-closed, solenoid-controlled valve. The actuation of the solenoid is effected electronically by a switching circuit in response to actuation of a switch, with the valve being open at a controlled, predetermined time interval for feeding fuel from a fuel source to the combustion chamber.
The drawback of this tool consists in that at variations of the admission pressure in the fuel source, the flow velocity of fuel varies, and a precise amount of fuel cannot be metered-out.
Accordingly, an object of the invention is to provide a setting tool of a type discussed above in which the drawbacks of the prior art tools are eliminated.